Method for manufacturing a biocompatible wire

ABSTRACT

The disclosure relates to a method for manufacturing a biocompatible wire, a biocompatible wire comprising a biocompatible metallic material and a medical device comprising such wire.The method for manufacturing a biocompatible wire comprises providing a workpiece of a biocompatible metallic material, cold working the workpiece into a wire, and annealing the wire, wherein a cold work percentage is 97 to 99%, wherein the cold working is a drawing with a die reduction per pass ratio in a range of 6 to 40%, and wherein the annealing is done in a range of 850 to 1100° C.

CROSS-REFERENCE TO RELATED APPLICATION

This Utility Patent Application is a continuation application of U.S.Ser. No. 16/749,495, filed Jan. 22, 2020, which is incorporated hereinby reference.

BACKGROUND

The disclosure relates to a method for manufacturing a biocompatiblewire, a biocompatible wire comprising a biocompatible metallic materialand a medical device comprising such wire.

There are many conventional methods for manufacturing a biocompatiblewire, which can be still improved.

SUMMARY

Hence, there may be a need to provide an improved method formanufacturing a biocompatible wire, which in particular allows toachieve a wire with improved fatigue life.

The problem of the present disclosure is solved by the subject-mattersof the independent claims, wherein further embodiments are incorporatedin the dependent claims. It should be noted that the aspects of thedisclosure described in the following apply also to the method formanufacturing a biocompatible wire, the biocompatible wire comprising abiocompatible metallic material and the medical device comprising suchwire.

According to the present disclosure, a method for manufacturing abiocompatible wire is presented. The method for manufacturing abiocompatible wire includes the steps of providing a workpiece of abiocompatible metallic material, cold working the workpiece into a wire,and annealing the wire. A cold work percentage is 97 to 99%. The coldworking is a drawing with a die reduction per pass ratio in a range of 6to 40%. The annealing is done in a range of 850 to 1100° C.

The present manufacturing method for a biocompatible wire can beconsidered as an optimized thermo-mechanical process including drawingand annealing steps to produce an improved biocompatible wire. The wiresmanufactured by the present manufacturing method can have an improvedfatigue life through smaller grain sizes and a specific grain sizedistribution of the wire material and/or a controlled number ofdislocations and twins in the crystal structure of the wire. The wiresmanufactured by the present manufacturing method can have a higherductility and a higher ultimate strength.

The wires manufactured by the present manufacturing method can be usedfor medical applications and in particular to produce coils, strands andthe like for medical applications. The medical applications can beCardiac Rhythmic Management (CRM), neurostimulation, neuromodulation,Deep Brain Stimulation (DBS) and the like.

The biocompatible wire can be made of or include biocompatible metallicmaterials and alloys, as for example MP35N® and MP35NLT™ alloy (35%Co-20% Cr-35% Ni-10% Mo with low titanium). The term “biocompatible” canbe understood as a quality of not having toxic or injurious effects onbiological systems, an ability of a material to perform with anappropriate host response in a specific application, a comparison of atissue response produced through a close association of an implantedcandidate material to its implant site within a host animal to thattissue response recognized and established as suitable with controlmaterials, refers to the ability of a biomaterial to perform its desiredfunction with respect to a medical therapy, without eliciting anyundesirable local or systemic effects in the recipient or beneficiary ofthat therapy, but generating the most appropriate beneficial cellular ortissue response in that specific situation, and optimizing theclinically relevant performance of that therapy and/or as a capabilityof a prosthesis implanted in the body to exist in harmony with tissuewithout causing deleterious changes.

In an embodiment, the biocompatible metallic material is an alloycomprising the following components: Cr in the range from about 10 toabout 30 wt. %; Ni in the range from about 20 to about 50 wt. %; Mo inthe range from about 2 to about 20 wt. %; Co in the range from about 10to about 50 wt. % and optionally less than 0.01 wt. % Ti. In anembodiment, the Cr, Ni, Mo and Co components are major constituents ofthe alloy with at least about 95 wt. % of the alloy being Cr, Ni, Mo andCo.

After the first cold working and the first annealing (described above),at least a second cold working and/or a second annealing can follow.There can also be at least an initial cold working and/or an initialannealing before above described first cold working and the firstannealing.

The cold work applied to the material decides the geometrical and themechanical attributes of the wire, as for example its strength. A lastand final cold working step defines a final strength of the wire.

The annealing allows the wire to soften, which might be particularuseful to further process the wire to a smaller diameter if needed. Theannealing involves parameters of temperature and time, which can dependupon prior deformation and type of material. In case the wire is made ofMP35N® and MP35NLT™ alloy, the annealing can be done in the range of1000° C. to 1100° C. In case the wire is made of an MP35N® and MP35™alloy cladded with Ag, the annealing can be done below the melting pointof silver, which is around 960° C. When reducing a diameter of the wire(e.g. by drawing), a duration of the annealing step can be reduced from,e.g., minutes to seconds. Further, the process can be changed from batchannealing to strand annealing. For strand annealing, the amount of timethe wire spends in a furnace for annealing can be in the order of fewtenths of a second.

In an embodiment, the drawing is a full die drawing. The drawing mayalso be a half die drawing. In an embodiment, the drawing is done with adeformation factor in a range of 1.2 to 2.0 and a contact length betweenthe workpiece and a drawing tool in a range of 0.5 to 0.2 mm. In anembodiment, the drawing is done with a speed in a range of 15 to 150m/min. In an embodiment, the initial diameter before drawing is in arange of 3 to 5 mm and/or a diameter of the wire after drawing is in arange of 0.1 to 0.9 mm. In an embodiment, the annealing is done for 750to 1500 seconds. In an embodiment, the method for manufacturing abiocompatible wire further includes an additional drawing after theannealing with a cold working percentage of 95 to 97%.

The present disclosure deals with the influence of drawing practicesnamely Full Die Drawing (FDD) and Half Die Drawing (HDD) on themechanical and electrical properties, deformation homogeneity, plasticinstability, strain rate sensitivity, strain rate hardening and cyclicfatigue behavior of MP35N® and MP35NLT™ wires, drawn to different coldwork (CW) reductions. The properties are associated and compared againstits microstructure, which has been characterized by FESEM, SEM, EBSD,and TEM.

The FDD drawing proves involved receding the cross-sectional area of thewire at a reduction per pass ratio of 20-30%, with the die semi-angle(α) of 6-8° and by controlling the Δ (deformation factor) value in therange of 1.2-2.0 and with the L value (i.e. the contact length betweenthe work piece and the die) in the range of 0.5-0.2 mm, when comparedwith the HDD wire drawing processes which generally involve drawing witha Δ value in the range of 2.5-5.0 and with the L being in the range of0.15-0.05 mm and at an reduction per pass ratio of 6-10%. The wire isdrawn from an initial diameter of 3.7 mm to 0.6 mm with a CW of 97-99%,using a single die drawing machine and Poly Crystalline Diamond (PCD)dies. For the MP35N® and MP35NLT™ wires, there was only one intermediateannealing applied after 97-99% CW at a temperature of 1050° C.-1100° C.using a spool to spool annealing machine for a duration of 900-1000seconds. The wire was further drawn to a diameter of 0.141 mm with a CWof 95-97% using a slip type multiple drawing machine using naturaldiamond (ND) dies and with varying drawing methods. The wires were drawnat a speed of 30 m/min to 100 m/min depending upon the diameter of thewire drawn, i.e., slower speeds for drawing big diameter wires andfaster speeds for drawing smaller diameters, and the wires are drawnusing an oil-based lubricant. The FDD method was completed in a shortertime with the total number of dies used being less than 10, while theHDD technique utilized 32-60 dies to complete the total cold workreduction of 98%.

According to the present disclosure, also a biocompatible wirecomprising a biocompatible metallic material is presented. Thebiocompatible wire includes a biocompatible metallic material which iscold worked from a workpiece and annealed. A cold work percentage is 97to 99%. The cold working is a drawing with a die reduction per passratio in a range of 6 to 40%. The annealing is done in a range of 850 to1100° C.

In an embodiment, the biocompatible metallic material is an alloycomprising the following components:

-   -   Cr in the range from about 10 to about 30 wt. %;    -   Ni in the range from about 20 to about 50 wt. %;    -   Mo in the range from about 2 to about 20 wt. %;    -   Co in the range from about 10 to about 50 wt. %.

In an embodiment, the Cr, Ni, Mo and Co components are majorconstituents of the alloy with at least about 95 wt. % of the alloybeing Cr, Ni, Mo and Co. In an embodiment, the biocompatible metallicmaterial further includes an additional component comprising at leastone of a group of Silver, Platinum, Tantalum, Gold, Copper and alloysthereof.

In an embodiment, the Cr, Ni, Mo and Co alloy forms a core and theadditional material forms a shell around the core when the wire is seenin a cross section. In another embodiment, the additional material formsa core and the Cr, Ni, Mo and Co alloy forms a shell around the corewhen the wire is seen in a cross section.

In an embodiment, the wire includes grains with a mean grain size in arange of 20 to 1000 nm.

In an embodiment, the wire has a yield strength in a range of 1300 to1900 MPa.

In an embodiment, the wire has an ultimate tensile strength in a rangeof 1700 to 2400 MPa.

In an embodiment, the wire has an essentially uniform grain sizedistribution along a cross section of the wire.

According to the present disclosure, also a medical device is presented.The medical device includes a wire as described above as a lead. Themedical device can be used for Cardiac Rhythmic Management (CRM),neurostimulation, neuromodulation, Deep Brain Stimulation (DBS) and thelike.

It shall be understood that the wire, the device, and the manufacturingmethod according to the independent claims have similar and/or identicalpreferred embodiments, in particular, as defined in the dependentclaims. It shall be understood further that a preferred embodiment ofthe disclosure can also be any combination of the dependent claims withthe respective independent claim.

These and other aspects of the present disclosure will become apparentfrom and be elucidated with reference to the embodiments describedhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the disclosure will be described in thefollowing with reference to the accompanying drawing:

FIG. 1 illustrates schematically and exemplarily an embodiment of amethod for manufacturing a biocompatible wire.

FIG. 2 illustrates schematically and exemplarily an embodiment of abiocompatible wire comprising a biocompatible metallic material.

FIG. 3 a : illustrates schematically and exemplarily an S-N curvecomparison between FDD and HDD wires drawn to 50% CW.

FIG. 3 b : illustrates schematically and exemplarily an S-N curvecomparison between FDD and HDD wires drawn to 75% CW.

FIG. 3 c : illustrates schematically and exemplarily an S-N curvecomparison between FDD and HDD wires drawn to 95% CW.

FIGS. 4 a -d: illustrate schematically and exemplarily grain sizedistributions of the MP35NLT™ wire drawn with the FDD drawing processfor different CW reductions.

FIGS. 5 a -c: illustrate schematically and exemplarily grain sizedistributions of the MP35NLT™ wire drawn with the HDD drawing processfor different CW reductions.

FIGS. 6 a -c: illustrate schematically and exemplarily a dislocationdensity of the MP35NLT™ wire drawn with the FDD drawing process fordifferent CW reductions.

FIGS. 7 a -c: illustrate schematically and exemplarily a dislocationdensity of the MP35NLT™ wire drawn with the HDD drawing process fordifferent CW reductions.

FIGS. 8 a -c: illustrate schematically and exemplarily a twin density ofthe MP35NLT™ wire drawn with the FDD drawing process for different CWreductions.

FIGS. 9 a -c: illustrate schematically and exemplarily a twin density ofthe MP35NLT™ wire drawn with the HDD drawing process for different CWreductions.

FIG. 10 : illustrate schematically and exemplarily a wire drawn with thenew drawing process and subjected to stress relief temperature of 875°C. for a dwell time of 3.1 seconds.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific examples in which the disclosure may bepracticed. It is to be understood that other examples may be utilizedand structural or logical changes may be made without departing from thescope of the present disclosure. The following detailed description,therefore, is not to be taken in a limiting sense, and the scope of thepresent disclosure is defined by the appended claims. It is to beunderstood that features of the various examples described herein may becombined, in part or whole, with each other, unless specifically notedotherwise.

FIG. 1 illustrates schematically and exemplarily an embodiment of amethod for manufacturing a biocompatible wire. The method formanufacturing a biocompatible wire includes the steps of:

-   -   S1. providing a workpiece of a biocompatible metallic material,    -   S2. cold working the workpiece into a wire, and    -   S3. annealing the wire.

A cold work percentage is 97 to 99%, the cold working is a drawing witha die reduction per pass ratio in a range of 6 to 40%, and the annealingis done in a range of 850 to 1100° C.

The drawing is a full die drawing. The drawing is done with adeformation factor in a range of 1.2 to 2.0 and a contact length betweenthe workpiece and a drawing tool in a range of 0.5 to 0.2 mm. Thedrawing is done with a speed in a range of 15 to 150 m/min. An initialdiameter before drawing is in a range of 3 to 5 mm and/or a diameter ofthe wire after drawing is in a range of 0.1 to 0.9 mm. The annealing isdone for 750 to 1500 seconds. The method for manufacturing abiocompatible wire may further include an additional drawing after theannealing with a cold working percentage of 95 to 97%.

The biocompatible wire can be made of or include biocompatible metallicmaterials and alloys, as for example MP35N® and MP35NLT™ alloy (35%Co-20% Cr-35% Ni-10% Mo with low titanium).

FIG. 2 illustrates schematically and exemplarily an embodiment of abiocompatible wire 10 comprising a biocompatible metallic material,which is cold worked from a workpiece and annealed, wherein a cold workpercentage is 97 to 99%. The cold working is a drawing with a diereduction per pass ratio in a range of 6 to 40% and the annealing isdone in a range of 850 to 1100° C. FIG. 2 further illustrates a medicaldevice 20 comprising such biocompatible wire 10 as a lead.

The biocompatible metallic material is an alloy comprising the followingcomponents: Cr in the range from about 10 to about 30 wt. %; Ni in therange from about 20 to about 50 wt. %; Mo in the range from about 2 toabout 20 wt. %; Co in the range from about 10 to about 50 wt. %. The Cr,Ni, Mo and Co components are major constituents of the alloy with atleast about 95 wt. % of the alloy being Cr, Ni, Mo and Co. Thebiocompatible metallic material further includes an additional materialcomprising at least one of a group of Silver, Platinum, Tantalum, Gold,Copper and alloys thereof.

The wire 10 includes grains with a mean grain size in a range of 20 to1000 nm. The wire 10 has a yield strength in a range of 1300 to 1900MPa. The wire 10 has an ultimate tensile strength in a range of 1700 to2400 MPa. The wire 10 has an essentially uniform grain size distributionalong a cross section of the wire.

The Cr, Ni, Mo and Co alloy may form a core 12 and the additionalmaterial may form a shell 11 around the core 12 when the wire is seen ina cross section. Otherwise, the additional material may form a core 12and the Cr, Ni, Mo and Co alloy may form a shell 11 around the core 12when the wire 10 is seen in a cross section.

Test Conditions

The amount of strain applied in the wire drawing process is defined bythe relation;

${\varepsilon = {2\ln\frac{d_{i}}{d_{f}}}};$

where d_(i) is the initial diameter and d_(f) is the final diameter, andthe SR is defined as the variation of strain over time. In the actualdrawing process, the SR applied on the material is differed by changingthe drawing speed, which changes the applied strain over time. Theamount of CW applied to the material is calculated as

${CW} = {1 - \left\lbrack \frac{D_{n}}{D_{1}} \right\rbrack^{2}}$

where D1 diameter of the first die and D_(n) is the nth die used.

The as-drawn wires were deformed in uniaxial tension as per ASTMstandard E8, using an Instron 6400 test frame, with a load cell of 500 Nand by pneumatic yarn grips. The cross-head speed was set at 12.7mm/min, and the gauge length was maintained at 254 mm for all thesamples tested. The testing was performed at room temperature, and thesamples were tested until fracture. The hardness test was performed asper ASTM standard A384-17, and the load was differed from 100 to 150 gbased on the diameter of the indented wire. The indentation wasperformed both in the longitudinal and transverse sections of the wire,and the indentation time was around 15-20 seconds for each sample. Fivepoints are intended along both the axis which is equidistant from eachother and evenly dispersed along their length. Hardness values wererecorded in Vickers Hardness Scale (H_(v)).

The electrical resistivity of the wires was measured using Burster 2316resistomat. The device accords to the proven 4-wire sensing method or by4-point probe method which is an electrical impedance measuringtechnique that uses separate pairs of current-carrying andvoltage-sensing electrodes to make more accurate measurements thantraditional two-terminal sensing. For each CW % condition, wire samplesof lm long were cut and clamped between the two connecting ends of theclamping device. The wires have been tested at room temperature with thetemperature compensation set to 20° C. and the resistivity data recordedin units of ohm/m. The obtained values are then converted into theconductivity measurements and plotted in SI derived units ofSiemens/meter.

The wire specimens drawn with different drawing practices are subjectedto cyclic fatigue tests on a rotary beam fatigue tester (RBFT) as perASTM standard E2948-16a. The tests were conducted on a custom-builtfatigue test machine by Heraeus. Before the fatigue loading, the drawnwires were straightened by a roller straightening machine, to remove theresidual curvature known as “cast,” in the wire which is a geometricalattribute inherited from the cold wire drawing process. This step needsto be done to minimize the variation in the test data, and it wasobserved during the fatigue set-up that the wires without straighteningwould spin out of the chuck and fracture at the chucks leading toerroneous results. The straightened wires were cut to the desired lengthbased on the input variables of the chuck distance, wire diameter,young's modulus (E), applied stress and the length of the wire wasdetermined from the respective calculations stated in the standardE2948-16a. One end of the wire is clenched to a hollow bush, and theother end of the wire is clamped to a rotating chuck which rotates at aspeed of 3000 RPM and operates at a frequency of 50 Hz. The vibrationsupports are mounted along the curvature of the wire, and the breakdetection probes are placed along the wire. A cyclic counter fixed tothe machine records the number of cycles to failure, and for eachrevolution of the chuck, the wire specimens are subjected to analternate compression and tension cycles during its course of cyclicloading. The tests were performed at room temperature using air as amedium.

Full Die Drawing (FDD) and Half Die Drawing (HDD)

MP35NLT™ wires drawn with different drawing practices namely the FDD andHDD; by varying the amount of deformation per pass induced on the wire,contributed to a wire with different mechanical and work hardeningcharacteristics in the material. The plastic instability and the strainrate sensitivity of the materials also varied significantly with thechange of deformation process. The wires drawn with the FDD drawingprocess contributed to a higher strength and ductility in the materialwhen compared to the HDD drawn wires for a similar CW reduction. Asoftening effect in the material was observed in the wires drawn withFDD practice between 75-90% CW, which led to a reduction of materialstrength and increased ductility after which it increased again. Thisphenomenon was attributed to the “Inverse Hall Petch Effect. Thedeformation homogeneity was higher for the FDD drawn wires, due to thelowered inhomogeneity factor, because of the uniformity in the grainsize and the microstructure gradient across the wire. The plasticinstability (PI), which determines the load bearing capacity or theresistant to necking was lower in the FDD wire until 75% CW, after whichit increased upon increase of reduction to 95%. The increase in PI wasascribed to the formation of shear bands in the FDD drawn wire, whichled to increased plastic strain localization in the material, due to theexhaustion of the dislocation density with the reduced grain size. Thelower PI until 75% CW was attributed to the higher twin density, andlower twin spacing seen in the FDD wire, which accorded to a higherstrain rate work hardening (SRWH) and strain rate sensitivity (SRS) inthe wire, which delayed the onset of necking and enhanced ductility inthe wire. The Strain Rate Sensitivity (SRS) or m value, of the FDD drawnwire decreased with the increase of SR, due to the reduction in thedislocation-based activities and increased GB shearing and diffusion inthe deformed wire. The twin spacing increased with the increase of SRfor the FDD drawn wire, thus contributing to a lower m. However, withthe HDD drawn wire, at an SR of 10⁻⁶s⁻¹, the value of m, was 65% lowerthan the FDD value. The reason for such a low SRS value has beenattributed to the increased localized strain concentration in thematerial, leading to the formation of shear bands in the material whichreduces the capability of the material to resist necking and thusreducing the ductility of the material. An abnormal hardening effect wasobserved in the HDD drawn subjected to an SR of 10⁻²s⁻¹, the stage IIhardening peak originated at a high strain, instead of its normalcommencement at low SR, after the dynamic recovery. This effect was dueto the solute segregation of the Mo atoms to the GB, as observed by theincreased concentration of the Mo in the deformed structure, whichincreased the strength and the hardening capacity of the wire.

The Low Cycle Fatigue (LCF) and High Cycle Fatigue (HCF) performance ofthe FDD drawn wire was remarkably higher than the HDD drawn wire until75% CW. The enhanced LCF performance for the FDD drawn wire, isattributed to the higher ductility in the wire, because of the highernumber of coherent twin boundaries (CTB) noticed in the FDD drawn wire;this allowed the dislocation to penetrate and slip through them, thusincreasing the endurance limit of the wire. The FDD drawn wire also hada smaller grain size when compared to the HDD wire, which contributed toincreased strength and higher dislocation density in the wire, thusbestowing to an improved HCF performance. The post fatiguedmicrostructure of the FDD wire also exhibited a dislocation cell andvein structure with several nanotwins embedded between the grainboundaries (GB) and the dislocation pile-up. There was a substantialdecrease in the LCF and HCF performance of the FDD wires, upon increaseof CW to 95%, there were shear bands observed in the microstructure ofthe FDD drawn wire, which increased the strain localization and areduced fatigue endurance. There were no striations observed in the FDDdrawn wire in both the LCF and HCF wires, this is because of the reducedductility in the wire, due to the formation of shear bands. Thefractured samples exhibited a brittle cleavage fracture, whereas the HDDwire displayed a dimple striation fracture with a dislocation cellstructure with nanotwins embedded at the interface of the GB.

Based on the above observations it can be concluded that the reductionof the grain size to a nanometer scale can be obtained at a lower CWreduction and a higher annealing temperature unlike the prior art.Higher mechanical properties can be obtained in the wire through anoptimum control of microstructure and their characteristics such asdislocation density and twin density. The plastic instability studieshave given valuable information on the materials response to deformationand their limitations to the applied strain during the drawing process.The strain rate simulation studies which were the first of its kind tobe done on this material till date, have led to crucial information inexhibiting the material response when subjected to different speedsduring the wire drawing process.

Cyclic Performance

The influence of drawing practices namely Full Die Drawing (FDD) andHalf Die Drawing (HDD) on the cyclic performance of MP35NLT™ wires havebeen investigated, by differing the amount of plastic strain applied onthe material. The as-drawn wires were subjected to rotary beam fatiguetests (R=−1) with varying stress amplitudes, and the microstructuralfactors controlling the Low Cycle Fatigue (LCF) and High Cycle Fatigue(HCF) performance were determined through post fatigued TEMinvestigations. So, the purpose is to characterize the influence of thedrawing practices on the cyclic response or fatigue behavior of theMP35NLT™ wires, drawn to varying cold work (CW) reductions and correlatea link between the process, microstructure, and fatigue.

Five specimens for each stress amplitude are tested between 500-1500 MPawith a stress ratio of R=−1. Six lots (three from FDD and three fromHDD) are tested for the 50% CW condition, and four lots (two from FDDand two from HDD) are tested for the 75 and 95% CW conditions. Therunout or the endurance limit for the condition is determined only ifall the five samples reach the 30 million (30 M) cycles. Thepost-fatigued specimens are collected and appropriately identified forfurther microstructure characterization by Transmission ElectronMicroscope (TEM).

The starting diameters of the material used for the fatiguecharacterization was 0.62 mm and 0.141 mm respectively, and the materialwas prepared in a fully annealed condition. Three different samplesnamely 50%, 75% and 95% CW are manufactured by varying the total areareduction. The 0.141 mm annealed wire was drawn to a diameter of 0.101mm to obtain the 50% CW samples; however, for the 75% and 95% CWsamples, the 0.62 mm wire was drawn to a diameter of 0.318 and 0.141 mmrespectively. The detailed description of the drawing process for thewires drawn to different CW reductions is illustrated in Table.

TABLE 1 Experimental detail comparison of the FDD and HDD wire drawingprocess. Start End Number of Passes Area Reduction (%) per pass ColdWork Diameter (mm) Diameter (mm) FDD HDD FDD HDD (CW) (%) 0.62 0.62  0 00 0  0  0.141 0.101 1 1 Pass 1: 48.6 Pass 1: 50.1 50 0.62 0.317 1 2 Pass1: 73.6 Pass 1: 46.7 75 Pass 2: 50.2 95 0.62 0.141 3 5 Pass 1: 66.8 Pass1: 46.7 Pass 2: 68.7 Pass 2: 48.7 Pass 3: 49.7 Pass 3: 53.6 Pass 4: 36.7Pass 5: 33.2

The cyclic data collected from the Rotary Beam Fatigue Tester (RBFT)tests are plotted in an S-N_(f) (Wohler) curve as illustrated in FIG. 3, where the S represents the stress amplitude, and N_(f) represents thenumber of cycles to failure. It can be observed from FIG. 3(a), that thefatigue performance of the 50% CW FDD drawn wires was significantlyhigher than the HDD wires in both the low cycle fatigue (LCF) and highcycle fatigue (HCF) regimes. The runout (30 million cycles) achieved fora stress amplitude was indicated for the tested batch of wire, with therespective color-coded arrow. It can be noticed that in FDD drawn wiresthe runout stress amplitude in the HCF region was around 670-780 MPa,whereas the runout stress level for the HDD drawn wire was around525-585 MPa. The LCF fatigue performance of the FDD drawn wires was alsoexceptionally higher than the HDD drawn wires with many specimens ableto withstand over 1 million (1 M) cycles, when tested between 1170-850MPa stress amplitudes, however for the HDD drawn wires, the wirespecimens could reach a fatigue endurance of 1 M cycles only at a stressamplitude of 670 MPa.

With the increase of CW to 75% as illustrated in FIG. 3(b), theperformance gap between the two drawn wires reduced, the FDD drawn wirescould reach the runout at a stress amplitude 530-760 MPa, and the HDDdrawn wires reached runout between 460 to 685 MPa. The LCF performanceof the HDD drawn wires also improved when compared to the 50% CWconditions, there were multiple specimens which were capable ofwithstanding 1 M cycles, in the stress range of 850 to 970 MPa. However,with the FDD drawn wires; nearly all the samples could reach 1 M cycles,and a few of them could even reach the runout of 30 M cycles at suchhigh stress. Further increase of CW to 95%, improved the fatiguebehavior of the HDD drawn wires both in the HCF and LCF regions whencompared to the FDD drawn wires. The FDD wires reached the runout at astress level of 1036 MPa whereas the HDD drawn wire could withstand thefatigue life of 30 M cycles at a stress amplitude of 1110 MPa. The LCFperformance of the HDD drawn wire was also observed to be significantlyhigher than the FDD drawn wire, with the HDD wires capable ofwithstanding the 1 M cycles at a stress amplitude of 1200 MPa, with anaverage fatigue life of 16-23 M. However, the FDD drawn wire had anaverage fatigue life of 2.7-9 M only. The LCF performance of the HDDwire between the stress amplitude of 1400-1550 MPa was also on anidentical note, with the HDD drawn wire outperforming the FDD drawn wireas illustrated in FIG. 3(c).

It is acknowledged that the prior deformation history or the method usedto process the material to its finished size, influence the propertiesof the material. In the current study, by keeping the total areareduction or the total plastic strain constant, the amount ofdeformation reduction per pass has been differed to study the influenceof the drawing method on the cyclic response of the MP35NLT™ wires. Thefatigue performance of the FDD drawn wires were comparatively higherthan the HDD drawn wires, in both the LCF and HCF regimes. The LCF andHCF behavior of the materials subjected to cyclic loading is dependenton the properties of the wire such as tensile strength, yield strength,and ductility, which are interrelated to the intrinsic microstructuralparameters such as grain size, dislocation density, twin density, andthe slip behavior. As seen in FIGS. 4 a -d, the grain size (GS) of theFDD drawn wire was in the range of 100-500 nm, whereas the HDD wire GSwas in the range of 700-1500 nm as in FIGS. 5 a -c.

The smaller GS contributed to the increased strength of the material,where the FDD drawn wire had higher strength than the HDD wire. Since itis well acknowledged that in the HCF region, where the applied stressamplitudes are low, the fatigue behavior of the material is dominated bythe crack initiation and most of the time is spent in initiating acrack, rather than propagating a crack which accounts for the totalfatigue life. So, with smaller grain size, the residual stressdistribution is more homogenous and spread over many grains in the FDDwire, which increased the fatigue resistance in the HCF region.

The LCF behavior of the FDD drawn wire was also better than the HDDwire, even though the GS is smaller for the FDD drawn wire, as the LCFperformance is noticed to be enhanced with coarser grain size. At anapplied stress amplitude of 1170 MPa, the average no of cycles tofailure (N_(f)) for the three batches of FDD wire were, 3×10⁴, 8×10⁵ and4×10⁶ cycles; however, it was only 1×10⁴ cycles for all the threebatches of HDD wire tested. Even with the decrease of the stressamplitude to 853 MPa, which is considered as lower specification of theapplied stress amplitude in the LCF region, the no of cycles to failureslightly improved for the HDD drawn wire with the N_(f), being 4×10⁴,4.8×10⁴ and 7×10⁴, and 1×10⁵, 7×10⁵, and 1×10⁶ for the FDD drawn wire.

Grain Size and Microstructure

Faster reduction of the grain size to a nanometer size and severelydeformed structure with high dislocation and twin density was obtainedin MP35NLT™ and MP cladded wires drawn with FDD drawing practice, for asimilar CW reduction. FIGS. 4 a-d illustrate the TEM images of the grainsize and microstructure of the FDD drawn wire drawn to different CWreductions and FIGS. 5 a-c illustrates the grain size and themicrostructure of the HDD drawn wire. The smaller grain size and thehigher dislocation and twin density as illustrated in FIGS. 6 a-c andFIGS. 7 a-c contributed to higher strength and ductility in the materialwhen compared to HDD wire as illustrated in FIGS. 8 a-c and FIGS. 9 a-c. The grain size linearly decreased with the increase of strain butthe amount of decrease of the grain size was higher in the materialdrawn with FDD drawing process.

The dislocation and twin density were observed to be higher in the FDDdrawn wire than the HDD drawn wire for a similar comparison of theapplied strain and the dislocation and twin density increased with theincrease of strain.

Y_(S) (Yield Strength) and the UTS (Ultimate Tensile Strength)

The current disclosure describes the impact of the drawing technique onthe mechanical properties of the wire like the Y_(S) (Yield Strength)and the UTS (Ultimate Tensile Strength) whereby higher mechanicalproperties especially the yield strength of the wire was obtained in theFDD drawn wire when compared to the HDD drawn wire when subjected to asimilar CW reduction. A higher work hardening rate and differenthardening regimes are obtained with the MP35NLT™ material subjected toFDD drawing process.

Based on the above results it can be summarized that the work hardeningrate in the FDD drawn samples are relatively higher when compared to theHDD wires. The initiation or onsite of twin formation is observed at alower strain in FDD samples whereas the observation of twins is observedin HDD only at higher strains. So, it can be concluded that the FDDdrawing process has a stronger effect in reducing the grain size andcontributing to higher deformation twinning in the material, thuscontributing to higher work hardening rates and increased strength inthe wire.

Inhomogeneous Deformation

In metal forming processes, such as wire drawing, due to its highplastic deformation, there is a severe contribution of redundant work tothe stress flow in the work piece, which makes the distribution ofstress and strain to be non-uniform. This leads to a condition known as“Inhomogeneous Deformation” which brings about a heterogeneity in thetexture and microstructure of the wires, thus affecting the mechanicaland physical properties of the wire.

In the current work, the influence of the drawing practices on theinhomogeneous deformation was studied, by calculating the InhomogeneousFactor (IF).

The current disclosure also describes the impact of the drawingtechnique on the hardness distribution and stress inhomogenity acrossthe wire for wires subjected to different CW reduction. The hardnessvalues (H_(V)) of the FDD and HDD drawn wires subjected to different CWreductions along Axis-1 (Transverse direction) and Axis-2(Longitudinal). The hardness values measured across the wire crosssection were used to determine the inhomogeneity in the wire, theequation for calculation the inhomogeneity is defined as

${IF} = \left( \frac{H_{S} - H_{C}}{H_{C}} \right)$

where H_(S) is the hardness at the surface of the wire and H_(C) is thehardness at the center.

It was observed that the hardness value at the surface, was higher forthe FDD wires when compared to the HDD wire until 50% CW, and thegradient in hardness ΔH (Hardness at the surface-Hardness at the center)was higher for the HDD drawn wires until 75% CW, after which itdecreases until 95% CW. For the FDD samples, the hardness gradient forthe 50% and 75% CW samples was comparatively lower than the HDD drawnwires. To understand the reason behind the variation in the ΔH gradientbetween the FDD and HDD samples, EBSD and FESEM analysis were performedon the samples deformed to various CW %. The ΔH gradient decreased withthe increase of CW for both the FDD and HDD drawn wires, with thegradient being lower for the FDD wires and higher for the HDD wires.Microstructure and grain size analysis was repeated on the deformedsamples to understand for the drop in ΔH gradient. With the increase ofCW to 75% CW, microstructures of the wires drawn with differenttechniques appeared highly deformed, but the severity of deformation washigher for the FDD wire. With further increase of plastic deformation to95% CW, the increase of ΔH gradient for the 95% FDD wire was marginallyhigher than the 75% CW wire, but lower than the 50% FDD wire, while theΔH gradient decreased in the HDD wire. The IF value for the FDD drawnwire was lower than the HDD drawn wire, until 50% CW, after which thevariation minimized. The IF values increased from the center of the wireto the surface, but the relative increase was higher in the HDD wireswhen compared to the FDD drawn wires. At 75% CW the curves were verysimilar to each other and the gradient between the surface and thecenter for both the drawn wires was minimal with the HDD drawn wirehaving a slightly higher IF value at the surface, however at 95% CW theIF value and the hardness gradient of the HDD drawn wires increasedagain when compared to FDD drawn wires. The reason for the variation inthe hardness gradient in the wires drawn with different drawingpractices are rationalized to the different microstructural and grainsize distributions observed in the wires.

Based on the above findings, it can be concluded that the wires drawnwith FDD drawing practice have a homogenous deformation throughout thewire cross section as noticed by the uniform hardness andmicrostructural gradient observed between the center and the surface ofthe wire. The FDD drawn wires have also higher strength and hardnesswhen compared to the HDD processed wires. This explains as why a higherΔH gradient was observed for the HDD samples, when compared to FDDwires. The significant difference in the grain size distribution alongwith the microstructural gradient observed between the surface and thecenter of the wire, would have contributed to the difference in thestrength of the wire, with fine grains contributing to a higher strengthand hardness, and coarser grains contributing to lower values. Thiscorresponds well with the Hall-Petch relationship, on the increase ofstrength in the material with a decreased grain size. Smallermicrostructural gradient was observed for the FDD wires between thecenter and the surface of the wires, thus contributing to a smaller ΔHgradient. The higher IF value imply an existence of higher redundantwork in the work piece with increased level of non-homogenousdeformation. However, for the FDD wires the deformation and stressdistribution between the surface and the center of the wire surface wasuniform which contributed to uniform microstructure and hardnessgradient and lower IF values and thus homogenous deformation.

Electrical Properties

The current disclosure also studies the impact of the drawing method onthe electrical properties of the wire. Electrical conductivity is animportant property in the design of lead wires, and it is desirable forthe wires build into leads to have a high electrical conductance or lowelectrical resistance in the order of 5-50Ω. The reciprocal of theelectrical conductivity is termed as the electrical resistivity (ρ) andit measures the degree through which the conductor opposes the flow ofcurrent per unit length.

The electrical conductivity of the wire decreased with the increase ofCW % and the conductivity of HDD drawn wires are higher than the FDDdrawn wires until 70% CW, after which the gap between them lowered. Thiscan be attributed to the variation in the deformation mechanics of thewire drawn with different drawing practices, which lead to differentstrengthening and different microstructures in the wire. The HDD drawnwires had a lower amount of lattice defects (dislocations and twins) inthe microstructure when compared to the FDD drawn wires.

This explains why the HDD drawn wire had a higher electricalconductivity when compared to the FDD drawn wire. The results concludedthat increased strength in the material by the generation of defects inthe wire leads to a loss of electrical conductivity in the wire, due tothe increased scattering of the conductive electrons, which results in adecreased electron mean free path and increased reflective coefficient.

Plastic Instability (PI)

Metals when plastically deformed by traditional forming methods such asrolling, forging, extrusion, wire drawing, significantly improved thestrength of the material, however, the exceptional increase in strengthhas been compensated by the loss of ductility in many materials. Thishas been attributed to the flow localization in the material, whichcontributed to an expedited necking in the material during its tensiledeformation in monotonic test conditions. This localized phenomenon ofstrain localization causes the deformation inhomogeneous driving to aphenomenon called plastic instability (PI). It is considered being atrade-off between the strain hardening (γ) and the strain ratesensitivity (m) of the material which resists or delays the necking inthe material when subjected to a uniaxial tensile deformation. So, thecontrol of plastic instability in the material is very important from anengineering standpoint of view, especially when the grain size isreduced to nanoscale for the desired strength improvements On the onsetof the plastic instability, the material loses its load bearingcapacity, and the stress continues to decrease with the increase ofstrain, leading to a catastrophic fracture.

The PI in the materials is defined by the equation;

γ+m≥1   (1)

${{{where}{}\gamma} = {{\left( \frac{\partial\sigma}{\partial\varepsilon} \right)_{\overset{.}{\varepsilon}}{and}m} = {\frac{\partial\left( {\ln\sigma} \right)}{\partial\left( {\ln\overset{.}{\varepsilon}} \right)}❘\varepsilon}}},{T.}$

The PI of the FDD wire is lower when compared to the HDD wire at 50% CWreduction, with the (γ+m) value being 0.462 for FDD wire and 0.314 forHDD drawn wire. The higher (γ+m) in FDD wire can be ascribed to thehigher strain hardening ability noticed in the FDD drawn wire whencompared to the HDD wire where a γ value of 0.435 was obtained for theFDD drawn wire, whereas the HDD wire had a smaller γ value of 0.303. Theresults corresponded well to the higher strain rate sensitivity values(m) observed in the FDD drawn wire when compared to the HDD drawn wire(m=0.027 for FDD and m=0.011 for HDD). By increasing the total areareduction to 75%, the (γ+m) value for both the FDD and HDD drawn wiresurged with the increase of deformation to 75% CW, with the gain beinghigher for the HDD wire (60%) than the FDD wire (11%) when compared tothe results at 50% CW. The FDD drawn wire had a γ of 0.473 and m of0.044, which led to (γ+m) value of 0.517, unlike the HDD drawn wirewhich had a (γ+m) value of 0.501, with γ and m values being 0.462 and0.039 respectively. On further increase of CW reduction to 95% it can beobserved that the (γ+m) value of the FDD drawn wire decreasedsignificantly from a value of 0.517 at 75% CW to 0.295. However, for theHDD drawn wire, the decline in the (γ+m) value was lower from a value of0.501 to 0.393.

Strain Rate (SR)

The effect of strain rate (SR) on the strain rate sensitivity (SRS),strain rate work hardening (SRWH) in Co-35Ni-20Cr-10Mo alloy (MP35NLT™)wires, subjected to drawing practices namely Full Die Drawing (FDD) andHalf Die Drawing (HDD) is analyzed and reported. The deformationresistance or the fracture mechanics in the material subjected toplastic deformation are determined by its grain size, the applied strainrate and its processing temperature. As the strain rate determines theloading sensitivity of the material over time, the understanding of theplastic behavior of the metal when subjected to different strain ratesis of great importance for ensuring the dependability and endurance ofthe material, during its service. The influence of the strain rate onthe plastic deformation of the metals is determined by a parametercalled Strain Rate Sensitivity (SRS) which is defined by

${m = {\frac{d\ln\sigma}{d\ln{\varepsilon \cdot}}❘\varepsilon}},T,$

where σ is the applied stress and

is the applied strain rate for a given strain and temperature. The wireswere subjected to a deformation strains of 0.64 (50% CW), and thesamples collected for the particular strain are subjected to uniaxialtensile tests at room temperature, by varying the strain rate.

The stress of the wire increased with the increase of strain rate from10⁻⁶s⁻¹ to 10⁻²s⁻¹ in both the FDD and HDD drawn wires, but the relativeamount of increase in stress for an amount of strain is higher in theFDD drawn wire when compared to the HDD drawn wire. The FDD drawn wirehad a strength of 2015 MPa, when subjected to a strain rate of8.3×10⁻⁶s⁻¹ and increased to 2100 MPa when the strain rate wasincremented to 3.3×10⁻²s⁻¹, however in the HDD drawn wire, the strengthof the wire was only 1870 MPa, at the lower strain rate and increased to2020 MPa with the elevation in strain rate. There was a significantdifference observed in the hardening behavior of the FDD and HDD drawnwire, for the applied strain rate. The FDD drawn wire exhibited a singlestage hardening regime, at a lower strain rate of 8.3×10⁻⁶ and displayeda three-stage hardening regime between the strain rates of 8.3×10⁻⁵s⁻¹to 3.3×10⁻²s⁻¹, with the stage II peak increasing with the increase ofstrain rate. However, in the HDD drawn wire the material exhibited asingle stage hardening curve up to a strain rate of 1.6×10⁻³s⁻¹ anddisplayed an abnormal three stage hardening curve at a strain rate of3.3×10⁻²s⁻¹. It was also noticed that the normalized hardening valuesfor the FDD drawn wire are comparatively higher than the HDD drawn wirefor a similar strain rate applied. This was attributed to the increaseddislocation density, reduced twin thickness, and a reduction in theGrain Boundary (GB) mechanisms such as GB sliding and shearing with theincreased SR, due to decreased dislocation cell sizes and reduced pileup the GB. The Strain Rate Sensitivity (SRS), or m value of the FDDdrawn wire decreased with the increase of SR, due to the reduction inthe dislocation-based activities and increased GB shearing and diffusionin the deformed wire. The twin spacing increased with the increase of SRfor the FDD drawn wire, thus contributing to a lower m. The m valuelinearly decreases with the increase of the strain rate for the FDDdrawn wires, however for the HDD wire, the m value increases up to astrain rate of 10⁻⁵ s⁻¹ and then decreases with the increase of strainrate as in FDD samples. It could be seen that the FDD drawn wire had ahigher m value when compared to the HDD drawn wire. The HDD drawn wireexhibited a different deformation mechanism with varying SR. At an SR of10⁻⁶s⁻¹, the strength and hardening of the material was significantlylower than the samples tested at other SR. TEM investigations, confirmedthat in the low SR deformed sample, due to the absence of priordislocations in the microstructure, the dislocation conciliated plasticdeformation activities were absent in the material, which made thedeformation intergranular due to the enhanced GB activities such as GBsliding. This limited the ability of the material to resist the largestrains and thus promoting an extremely localized deformation, resultingin the formation of shear bands in the microstructure which made thedeformation highly inhomogeneous and contributing to severe plasticinstability in the material. This reduced the work hardening andload-bearing capacity of the material thus contributing to lowerstrength, ductility and a reduced SRS. An abnormal hardening effect wasobserved in the HDD drawn subjected to an SR of 10⁻²s⁻¹, the stage IIhardening peak originated at a very high strain, instead of its normalcommencement at low SR, after the dynamic recovery. This effect wasaccredited to the solute segregation of the Mo atoms to the GB, asobserved by the increased concentration of the Mo concentration in thedeformed structure, which increased the strength and the hardeningcapacity of the wire.

The fracture morphology of the FDD samples looked different whencompared to the HDD samples, with the low SR deformed FDD drawn wiresexhibiting a higher fraction of the dimpled area and bigger dimple sizeand vice-versa. The dimpled region between the surface and the center ofthe wire looked homogeneous in size and shape. The fractographyobservations correlated well with the mechanical results of higher m andincreased ductility seen in the FDD wire at a lower SR, which confirmsthe FDD drawn material to have higher resistant to necking, because ofits higher SRS and higher hardening rate than the HDD wire.

However, with the HDD drawn wire, the fractography observation of thelow SR samples exhibited smaller dimple size and a reduced fracturedarea, the fractured area also displayed a combination of shear andductile mode fracture. The dimple size at the surface of the wire wassmaller when compared to the center, and the deformation lookedinhomogeneous.

Stress Relief

The disclosure also explains that MP35NLT™ and MP35NLT™/Ag wires drawnwith different filling ratios in the range of 15-41%, when subjected toa prior CW of 95-96% and drawn to a final diameter and subjected to afinal stress relief operation in the range of 800-900° C. with a dwelltime of 2-3 seconds led to a reduction in the EL % and an improvement inthe YS and the UTS of the wire, but the reduction of EL was gradual withtime and the properties of the wire needed two weeks for stabilization,with higher stress relief temperature contributing to a higher drop whencompared to a lower temperatures as illustrated in Table 3, and alsocontributing to a higher YS/UTS ratio of >0.9.

The wires drawn with the FDD drawing process produced a microstructurewith coarse grains at the surface of the wire and fine grains at thecenter as illustrated in FIG. 10 with a randomly orientedmicrostructure.

TABLE 2 Mechanical data of the lots drawn with the FDD drawing processand subjected to stress relief. Properties of the wire Properties ofafter stress the wire relief with aging duration Final Dwell StressStress prior to stress relief Aging Prior anneal time Final reliefrelief YS UTS time YS UTS Condition Material CW % temp (Seconds) CW %temp time (MPa) (MPa) EL % (days) (MPa) (MPa) EL % YS/UTS A MP Ag 95-96900 7.80 45-60 875 3.1 1309 1516 2.58 0 1382 1476 2.24 0.94 25% 7 14331509 2.20 0.95 14 1442 1506 2.03 0.96 1455 1509 1.87 0.96 25 1459 15071.77 0.97 48 1466 1510 1.65 0.97 B MP Ag 95-96 950 7.80 45-60 875 3.11320 1537 2.51 0 1455 1547 2.13 0.94 25% 7 1456 1547 2.16 0.94 14 14601541 2.06 0.95 21 1474 1547 1.90 0.95 25 1475 1542 1.81 0.96 48 14791545 1.76 0.96 C MP Ag 95-96 875 7.80 45-60 875 3.1 1301 1519 2.73 01385 1478 2.33 0.94 25% 7 1415 1479 1.87 0.96 14 1437 1490 1.75 0.96 211451 1489 1.67 0.97 25 1459 1495 1.65 0.98 48 1462 1497 1.63 0.98 D MPAg 95-96 900 7.80 45-60 900 2.2 1338 1561 2.40 0 1444 1538 1.89 0.94 25%7 1464 1548 1.73 0.95 14 1482 1551 1.67 0.96 21 1489 1552 1.63 0.96 251490 1554 1.62 0.96 48 1496 1557 1.60 0.96 E MP Ag 875 7.80 45-60 9003.1 1385 1579 2.38 0 1396 1484 1.76 0.94 25% 7 1403 1494 1.72 0.94 141412 1494 1.66 0.95 21 1419 1498 1.62 0.95 25 1426 1500 1.60 0.95 481430 1505 1.58 0.95 F MP Ag 95-96 900 7.80 45-60 855 2.5 1260 1488 2.350 1343 1446 2.16 0.93 25% 7 1397 1486 2.08 0.94 14 1407 1483 1.96 0.95 21409 1479 1.83 0.95 G MP Ag 85-90 900 7.8  70-85 900 2.5 1456 1658 2.350 1282 1437 2.18 0.89 25% 7 1325 1470 1.89 0.90 14 1345 1494 1.75 0.90

The wires manufactured by the above process also led to a wire free fromthe inherent residual cast and lift present in the wire this leading toa straight wire on the spool without any mechanical damages induced bythe roller straightening processes. These types of wires can be used forwires needed for IV therapy and guiding systems for medical applicationswith an added advantage of high strength and kink resistance.

It has to be noted that embodiments of the disclosure are described withreference to different subject matters. In particular, some embodimentsare described with reference to method type claims whereas otherembodiments are described with reference to the device type claims.However, a person skilled in the art will gather from the above and thefollowing description that, unless otherwise notified, in addition toany combination of features belonging to one type of subject matter alsoany combination between features relating to different subject mattersis considered to be disclosed with this application. However, allfeatures can be combined providing synergetic effects that are more thanthe simple summation of the features.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive. Thedisclosure is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing a claimed disclosure, from a study ofthe drawings, the disclosure, and the dependent claims.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. A single unit may fulfil the functions of several itemsre-cited in the claims. The mere fact that certain measures are re-citedin mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage.

Although specific examples have been illustrated and described herein, avariety of alternate and/or equivalent implementations may besubstituted for the specific examples shown and described withoutdeparting from the scope of the present disclosure. This application isintended to cover any adaptations or variations of the specific examplesdiscussed herein. Therefore, it is intended that this disclosure belimited only by the claims and the equivalents thereof.

1. A biocompatible wire comprising a biocompatible metallic material,which is cold worked from a workpiece and annealed, wherein a cold workpercentage is 97 to 99%, wherein the cold working is a drawing with adie reduction per pass ratio in a range of 6 to 40 %, and wherein theannealing is done in a range of 850 to 1100° C. wherein the wirecomprises grains with a mean grain size in a range of 20 to 1000 nm. 2.The wire according to claim 1, wherein the wire has a yield strength ina range of 1300 to 1900 MPa.
 3. The wire according to claim 1, whereinthe wire has an ultimate tensile strength in a range of 1700 to 2400MPa.
 4. The wire according to claim 1, wherein the wire has anessentially uniform grain size distribution along a cross section of thewire.
 5. The wire according to claim 1, wherein the biocompatiblemetallic material is an alloy comprising the following components: Cr ina range from about 10 to about 30 wt. %; Ni in a range from about 20 toabout 50 wt. %; Mo in a range from about 2 to about 20 wt. %; Co in arange from about 10 to about 50 wt. %, wherein the Cr, Ni, Mo and Cocomponents are major constituents of the alloy with at least about 95wt. % of the alloy being Cr, Ni, Mo and Co.
 6. The wire according toclaim 5, wherein the biocompatible metallic material further comprisesan additional material comprising at least one of a group of Silver,Platinum, Tantalum, Gold, Copper and alloys thereof.
 7. The wireaccording to claim 6, wherein the Cr, Ni, Mo and Co alloy forms a coreand the additional material forms a shell around the core when the wireis seen in a cross section.
 8. The wire according to claim 6, whereinthe additional material forms a core and the Cr, Ni, Mo and Co alloyforms a shell around the core when the wire is seen in a cross section.9. The wire according to claim 1, wherein the drawing is a full diedrawing.
 10. The wire according to claim 1, wherein the drawing is donewith a deformation factor in a range of 1.2 to 2.0 and a contact lengthbetween the workpiece and a drawing tool is in a range of 0.5 to 0.2 mm.11. The wire according to claim 1, wherein the drawing is done with aspeed in a range of 15 to 150 m/min.
 12. The wire according to claim 1,wherein an initial diameter of the workpiece before drawing is in arange of 3 to 5 mm.
 13. The wire according to claim 1, wherein adiameter of the wire after drawing is in a range of 0.1 to 0.9 mm. 14.The wire according to claim 1, wherein the annealing is done for 750 to1500 seconds.
 15. The wire according to claim 1, wherein the annealingis followed by an additional drawing with a cold working percentage of95 to 97%.
 16. A medical device, comprising a wire according to claim 1,as a lead.